The present invention relates to the splicing or joining of electrical cables and, more particularly, to a novel, continuous method of manufacture of a shrinkable composite sleeve used in forming a splice or joint, to apparatus for practicing the method, to a novel, highly effective stress control material compatible with the semiconductive components of the sleeve and of the cable for which the splice or joint is provided, and to a method of manufacturing the stress control material.
A copending U.S. patent application of George Bahder Ser. No. 319,429, filed Nov. 9, 1981, and assigned to the assignee of the present invention, discloses a new type of splice or joint especially adapted for splicing high-voltage power cables. The joint comprises a shrinkable, composite sleeve and high-resistive stress control components of which one is an integral part of the composite sleeve and the other is a separate layer of high electrical resistivity and mechanically resilient characteristics.
Said patent application Ser. No. 319,429 discloses a method of producing the shrinkable sleeve in a sequence of separate operations. Specifically, the three-layer polymeric composite sleeve is manufactured in one or more extrusion and curing passes over a metallic core. In a subsequent, completely separate process, the previously hardened sleeve is chopped into small lengths which then are placed into separate cylindrical containers. One of the ends of the sleeve is sealed, internal pressure is applied by introducing a pressurized fluid through the other end, and the sleeve is heated in a temperature sufficient to allow for the softening and expansion of the sleeve. Subsequently, the expanded sleeve is cooled to room temperature. Since the ends of each sleeve have to maintain their original dimensions, in order not to loosen the seals, the sections of sleeve being set up for expansion have to be significantly longer than the useful length of the sleeves. Subsequently, a significant part of the total length is discarded, since only the part having uniform expanded dimensions is useful.
The nonuniform expansion along the length of sleeve requires careful control of the process. In particular, the timing for pressure application during the heating step becomes critical, in order to minimize cracks and voids.